This invention relates to a red light emitting gallium phosphide (GaP) device having a pn-junction.
The light emitting device of this type is comprised of an n-type GaP substrate formed by a liquid-encapsulated Czochralski (LEC) method, an n-type GaP layer formed on said GaP substrate by a liquid phase epitaxial (LPE) growth method, and a zinc and oxygen-containing p-type LPE layer formed on said GaP layer.
Conventionally, with respect to this pnn-structure device, various studies have been conducted to increase its luminescent efficiency, and the following techniques are presently known as representative examples. That is to say, U.S. Pat. No. 3,703,671 states, by paying attention to the oxygen concentration N.sub.O and acceptor concentration N.sub.A in a p-type LPE layer, that when N.sub.O = 1 .times. 10.sup.17 to 9 .times. 10.sup.17 cm.sup.-.sup.3 and N.sub.A = 2 .times. 10.sup.17 to 10.sup.18 cm.sup.-.sup.3, a high luminescent efficiency can be obtained. According to this U.S. patent application, the luminescent efficiency is increased by forming in the p-type layer a large number of zinc-oxygen nearest neighbor pairs each constituting a radiative center by doping the p-type layer with as much oxygen as possible and decreasing the carrier concentration of the p-type layer by compensating the acceptor with an oxygen donor which enhances the injection efficiency of the electron into the p-type layer. With respect to the donor, it is desirable, in order to increase the injection efficiency of electrons from the n-type layer into the p-type layer, that the donor concentration of the n-type layer be as high as possible, but where the donor concentration is too high, the light absorbing efficiency of the crystal is increased, so that the effect is increased that the luminescent light is reabsorbed into the crystal, to decrease the amount of light emitted into the device exterior. Said U.S. patent specification states, for the above-mentioned two reasons, that an optimum donor concentration ranges from 0.3 .times. 10.sup.18 to 1.0 .times. 10.sup.18 cm.sup.-.sup.3.